摘要:

Abstract—The effects of postirradiation incubation at 42°C on respiration and viability were studied in cells of ultraviolet (UV)‐irradiatedEscherichia colistrains B/r and B. Prior to UV irradiation (52 J/m2at 254 nm), the cells were grown in minimal liquid medium containing glycerol. When incubated in this liquid medium at 37°C, respiration of both strains is known to cease about an hour after UV irradiation, but is found to be continuous upon incubation at 42°C. In both strains, continuance of respiration is accompanied by an early increase in viability (‘liquid thermal reactivation’), but the increase for B/r (30‐fold) is 3 times that for strain B. The kinetic pattern of viability for B/r at 42°C is the same as that previously obtained for B/r and B when respiration is maintained by 5‐fluorouracil (FU) treatment. A different pattern is seen for Strain B at 42°C, but when FU and thermal treatments are given together, the FU type response dominates and the amount of reactivation obtained is about the same as with FU alone. This result suggests that in the absence of FU liquid thermal treatment prevents division of a potentially reactivable group of filaments in thislon‐strain. The amount of liquid thermal reactivation (where plates are incubated at 37°C) is about equal to the amount of plate thermal reactivation (where irradiated cells, plated immediately after UV irradiation are incubated at 42°C). We infer that liquid and plate thermal reactivation involves the

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06466.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—A plaque assay for adenovirus 2 on normal human fibroblasts has been developed and used to measure the survival of ultraviolet‐irradiated virus on six human fibroblast cell lines. When four xeroderma pigmentosum cell lines were used as viral hosts, an average of one lethal event per virus in the viral population was made with 10, 15, 62, and 78 J m‐2respectively, while using two normal cell lines as hosts, 197 and 205 J m‐2were required to inflict the same damage. These differences are attributed to the known repair deficiency of xeroderma pigmentosum cells, and are discussed in the light of previous data obtained using other animal

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06467.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—In bidistilled water, 4‐thiouridine (4TU) exhibits a weak unusual luminescence, the quantum yield of which is 3 × 10‐4at 25°C. The excitation spectrum corresponds well to the 4TU absorption spectrum. The emission lies at longer wavelengths (Λmax550 nm) than the 4TU phosphorescence observed at 77 K (Λmax, 470–480 nm). From the emission signal obtained after an excitation flash of 3 ns half‐width, an “apparent” rate constant for the radiative deactivation process, shorter than 5 × 106s, can be inferred. The 300 K emission is efficiently quenched by halides and by oxygen: quenching involves a long‐lived intermediate (⋍ 200 ns).Clearly the emissive state X is populated through the S0‐S1electronic transition π→π* of 4TU. The nature of X cannot be unambiguously determined: it cannot be an excimer but can be either the 4TU triplet state or another chemical state distinct from the 4TU excited singlet or triplet states.An interesting finding is that the 300 K emission and the ability of 4TU to photoreact are related: they are quenched with the same efficiency by halide anions. This indicates that quenching occurs atthe same long‐lived intermediate species, which is either a precursor of the

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06468.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—Photochemical and γ‐ray‐induced reactions of purines with amines are described. These lead to the appropriate 8‐substituted purines. The photoproducts were obtained in yields of up to 100% by the use of a variety of photosensitizers, including peroxides. A free radical mechanism is proposed for these reactions.Such reactions may be relevant to the problem of the nature of DNA‐protein cross‐links induced by ultraviol

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06469.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—The application of photoelectron microscopy as a general method of imaging organic and biological surfaces requires a knowledge of the photoelectric effect of very thin organic films. In this study, low magnification images of a 7 Å thick pattern of copper phthalocyanine were obtained, demonstrating that it is possible to visualize a monolayer of organic compound in photoelectron microscopy. Relative photoelectron currents were measured for a series of copper phthalocyanine films ranging in thickness up to 1900 Å. The relative photoelectron currents were independent of temperature (90–298°K), suggesting that electron‐electron and not electron‐phonon scattering is the dominant mechanism. The photoelectric properties measured are determined primarily by the large organic ring structure and not the central metal atom, as evidenced by the fact that substitution of metal‐free phthalocyanine for copper phthalocyanine did not substantially alter the values of observed photoelectron currents. An analysis of the data indicates the depth resolution is 15 ű 5 Å, and equals the electron mean free path. This very good depth resolution is a result of the low kinetic energy associated with electrons released by irradiation near the photoemi

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06470.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—Photosensitized oxidation of sarcoplasmic reticulum (SR) vesicle membranes by a series of xanthene dyes was investigated. With increasing dye concentration and illumination time, the calcium ion uptake, ATPase activity and UV fluorescence intensity of SR decreased, and the absorbance at 241 nm increased. In xanthene dyes, the order of inactivation of the calcium uptake and ATPase activity of SR was in accord with decreasing order, of fluorescence intensity and increasing order of absorbance at 241 nm. Some regular relationships exist between the molecular structures of xanthene dyes and the photodynamic inactivation of SR membrane

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06471.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—The proteins of spinach chloroplasts and their subfragments containing photosystem I and photosystem II, obtained by Triton X‐100 treatment or French‐pressure rupture, were separated by sodium dodecyl sulfate (SDS)‐acrylamide electrophoresis at pH 7·0 in phosphate buffer. The individual protein bands were identified where possible by comparing them with known, isolated and characterized proteins from chloroplasts, and their molecular weights were determined. The protein composition of the chloroplast fragments were correlated to the functional properties of these fragments. Distinct patterns were obtained for photosystem I and photosystem II particles. The major protein of photosystem II is expressed in the 23 kilodalton range and photosystem I proteins seem to be clustered mainly in the 50–70 kiloda

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06472.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—Chlorophyllaandband bacteriochlorophyllahave been incorporated in an oriented phospholipid multilayer. The orientation of the chlorophyll molecules in this layer has been measured by polarization spectroscopy. Formulas are given expressing the dichroic ratioRas a function of the angle of tilt θ between the molecule and the plane of the multilayer and the angle μ between this plane and the transition dipole moment measured in the plane of the molecule. The possibility of overlapping bands of mutually perpendicular polarization has been taken into account. Analysis of the experimental results gives the angles θ and μ as well as an estimate for the fraction of polarization of some bands along the dihydro axis in the plane of the chlorophyll mol

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06473.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—Delayed fluorescence from chromatophores of the photosynthetic bacteriumRhodopseudomonas viridiswas measured at temperatures below 0°C. A component with a decay half‐time of about 7 ms was found. Its intensity was directly proportional to the number of reaction centers in the P985+·A‐state. During prolonged illumination it faded as electrons moved forward along the electron transport chain from the primary acceptor, A, (P985+·A‐→P985+·A), and its decay in the dark paralleled the disappearence of the P985+electron paramagnetic resonance absorption. The data suggest that this component of delayed fluorescence results from a direct reversal of the primary light reaction. While the rate of the P985+middot;A‐→P985·A reaction was almost independent of temperature, delayed fluorescence intensity displayed an apparent activation energy of 0°2 eV. It is concluded that the P985+·A‐→P985·A reaction proceeds by parallel radiative and nonradiative routes. The direct proportionality between delayed fluorescence and the concentration of P985+·A‐pairs seems to preclude an involvement of triplet‐triplet annihilation or dependence of delayed fluorescence upon the vari

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06474.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Abstract—Electron spin resonance studies have shown that chlorophyll and bacteriochlorophyll can be photo‐oxidized in a variety of solvents via their lowest excited singlet states to produce cation radicals. Pheophytin does not undergo this reaction. The mechanism of this photoprocess and its implications for photosynthesis are discus

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1974.tb06475.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY